DE19713980C2 - Power diode, manufacturing process therefor and use thereof (FCI diode) - Google Patents

Description

The invention relates to a power diode consisting of egg nem semiconductor body

• - an inner zone of the first conduction type,
• - A cathode zone adjacent to the inner zone from the most conductivity type and higher doping concentration than in the inner zone,
• - An anode zone adjoining the inner zone of two th conductivity type and higher doping concentration than in the inner zone.

Such power diodes, which are also called pin diodes, have been known for a long time and for example by F. Kau ßen and H. Schlangenotto in "Current Developments fast switching power diodes ", 39th ETG technical report, VDE- Verlag, pages 25 to 40, Bad Nauheim, 1992, detailed be wrote.

An FCI diode (field-controlled injection) of the beginning called type is known for example as a read diode and of K. T. Kaschani and R. Sittig in "How to avoid TRAPATT- Oscillations at the Reverse Recovery of Power Diodes ", CAS'95, Pp. 571-574, Sinaia, 1995.

The read diode was originally developed as a high-frequency component for the generation of IMPATT vibrations. The FCI concept is explained below in FIG. 1 using the known read diode in the special embodiment as a pin power diode. Such a read diode is in particular from FIG. 5 of the above-mentioned publication by Kaschani et al. known.

The pin-power diode according to Fig. 1 shows a semiconductor body 1. The semiconductor body 1 consists of an n ^- -doped inner zone 2 . On the cathode side, the n ⁺ -doped cathode zone 3 is arranged on the inner zone 2 . The cathode zone 3 is connected to the cathode connection K via the cathode electrode 7 . An n-doped coupling zone 5 and a p ⁺ -doped anode zone 6 adjoin the inner zone 2 on the anode side. On the anode side, the anode zone 6 is connected to the anode terminal A via the anode electrode 8 .

As is apparent from Fig. 1, Zvi rule at the pin diode anode region 6 and the inner zone 2 a narrow Kopp lung zone 5 is inserted, the same conductivity type as the inner zone 2, but is more heavily doped than the inner zone 2. Due to this doping profile, the electric field in the blocking mode consists of a so-called high field zone and a so-called low field zone. Areas with a high electric field strength are designated with a high field zone and areas with a low electric field with a low field zone.

While the high field zone is limited to the narrow area of the coupling zone 5 immediately in front of the anode zone 6 , the low field zone extends almost homogeneously over the entire inner zone 2 . Depending on the level of the doping, however, the breakthrough field strength in the high field zone is significantly higher than in the low field zone (E _{BD, H} << E _{BD, L} ).

In order to ensure localized avalanche multiplication in the event of a voltage breakdown, the pin diode is dimensioned so that the field peak in the high field zone at this point in time reaches its breakdown field strength E _{BD, H} , while the field maximum in the low field zone is still far below its breakdown field strength E _{BD, L} located. If the breakdown voltage V _{BD is} exceeded, the charge carrier generation by avalanche multiplication occurs first only in the high field zone.

While the holes generated in this way flow off immediately at the adjacent p ⁺ -doped anode zone 6 , the electrons have to cross the entire space charge zone on the way to the n ⁺ -doped cathode zone 3 . The electrons move in the high field zone with saturation speed and due to their negative charge lead to a corresponding compensation of the space charges of the high field zone and the low field zone.

However, the effect of this compensation on the two zones is different. This leads to a reduction in the peak of the field and a reduction in avalanche multiplication in the high field zone, which in turn leads to a decrease in the electron current or its compensating effect on the space charge there. This negative feedback finally results in a stabilization of the field maximum near the breakdown field strength E _{BD, H,} regardless of the applied overvoltage.

The high field zone therefore serves both to provide the necessary charge carriers and to localize the avalanche multiplication. In the low field zone, on the other hand, the increasing compensation of the space charge by the increasing electrical current with increasing overvoltage leads to an increase in the gradient of the electrical field and thus to a corresponding increase in the electrical field, in particular in front of the cathode zone 3 .

The coupling of the electric fields from the high-field zone and the low-field zone takes place in the pin power diode accordingly in FIG. 1 via the space charge of the coupling zone S. However, the space charge coupling has proven to be unusable for the commutation of power diodes, since the space charge coupling is very strongly temperature-dependent . The use of such pin power diodes in practice is therefore unthinkable.

The object of the present invention is therefore to develop new FCI Provide and use diodes where the high Field zone with the low field zone almost independent of temperature is coupled.

According to the invention, this object is achieved by a power diode solved with the features of claim 1. A correspond The manufacturing process is specified in claim 9 ben, are uses for such FCI diodes mentioned in claims 10 to 13.

In the first embodiment of the invention, there is an interface che provided between the inner zone and the anode zone, the with the exception of the peripheral areas of the anode zone, where the Interface occurs on the surface of the semiconductor body, is at least partially curved. This measure will a sharply localized field increase causes what the one towards a high field zone and a low field zone speaks that is not coupled to space charges and therefore also are not strongly temperature-dependent.

In the second embodiment of the invention is in the inner zone at least one - in terms of potentials - Floating area of the same line type as in the inner zoo no By introducing such floating areas, the ty are typically much more heavily endowed than the inner zone itself, equipotential zones are established in the inner zone tet, which is a disturbance of the electrical field and thus in a certain localized field elevation in certain areas cause. This sharply localized field increase causes again the establishment of a local high field zone and one Niederfeld zone, which is also not coupled to space charges here are and therefore not strongly dependent on temperature subject to.  

Such power diodes are referred to below as FCI diodes designated with geometric coupling.

Pin power diodes with geometric coupling have against the advantage of pin power diodes with space charge coupling, that the commutation process is largely independent of temperature expires.

In addition, geometrically coupled FCI diodes point in the opposite Set an active, control over the conventional pin diodes overvoltage limitation, which is largely independent of storage charge, commutation speed and life permanent setting is, to no significant influence of pass-through, blocking and switch-on behavior leads and above still a significant reduction in switching losses leaves.

In a typical development of the invention, the floating areas at least partially to the anode zone. In this way it is ensured that the voltage through break directly at the p-n junction between the anode zone and the float the area takes place.

Typically, the floating areas are in the areas of the inner zone on the anode side. In a continuation the floating areas border at least partially the anode zone.

The interface between the inner zone is advantageous and the floating area is also curved. this causes also a disturbance of the electrical field and thus in a sharply localized field elevation in these areas. Like this the Hochfeld and Nierder are also included in these measures Field separated locally.

Because the floating areas in terms of their line property They can act like a short circuit in a training course  the invention also realized by conductive material the. As a conductive material because of its good guidelines ability and its easy handling in terms of process technology typically very highly doped polysilicon is used. It but are also other conductive materials such as Metals or metal silicides conceivable.

At least one can advantageously be in the semiconductor body antiparallel to the power diode and connected in series second, monolithically integrated diode may be provided. To can have a further zone on the anode side or cathode side Production of a second p-n junction can be provided. This zone typically has a higher doping concentration tration as the adjoining anode zone or catho denzone. In this way, as I said, a series can be created circuit from a geometrically coupled FCI diode and egg ner to her in the reverse direction connected further diode put. Through this monolithically integrated, anti-parallel arranged diode series connection, the Durchlaßbe drove the FCI diode suppress, so that it is now as pure Voltage limiter acts.

By connecting another diode in parallel, this can be done win an FCI hybrid diode arrangement, in which in through leave only the other diode and in blocking mode only the FCI diode is relevant. Is it another Tuesday or around a component with optimized transmission behavior, so can be minimized in this way at the same time Passage and switching losses and an optimization of Reach the commutation process.

For the preferred method of manufacturing the areas of An odzone with a curved p-n transition and the floating Ge offers in the inner zone are advantageously initially trenches in the surface of the semiconductor body etches. Then, after appropriate masking, the Surfaces of the semiconductor body the desired areas  who introduced the anode zone or the floating areas the. The doping is typically determined by a mas introduced diffusion or ion implantation. On  the trenches can be closed again by CVD, for example filled and planarized.

Geometrically coupled power diodes can be more advantageous as voltage limiter for voltages ≧ 500 V to Un suppression of transient overvoltages. The transient voltage limiters ("transient voltage supressor ", TVS) are on voltages ≦ 500 V be borders. Other comparable components, such as Varistors, do not respond quickly enough, tolerate them with frequent recurring voltage peaks do not lose or age faster than desired.

The FCIs according to the invention can be particularly advantageously Diodes also as free-wheeling diodes for power semiconductor components Use elements, such as in parallel Bipolar transistors, MOSFETs, IGBTs, GTOs, thyristors, MCTs, Etc.

The most critical operating state of a power diode The type mentioned above is the commutation, that is the Change from pass-through to blocking operation. When commuting must be in the pass mode for conductivity modulation Storage zone needed again within a very short time to be removed again afterwards reverse voltage to be able to record. This happens via the so-called Reverse current, which changes automatically when switching to blocking mode table.

Due to the influence of inevitable leakage inductances In practice, however, a power diode can only use one finite steepness can be commutated. To achieve high induc Avoid overvoltages and oscillations a power diode has a soft commutation behavior ten, called "soft recovery" behavior. Underneath one understands in particular one after reaching the reverse flow peak gently decaying backflow.  

The commutation behavior of a power diode after reaching it the backflow peak is characterized by the need the leakage inductance charged to the maximum reverse current fully unloaded again. To do this in the diode losses to be kept as low as possible this unloading process take place as quickly as possible. At the same time, however, soft recovery behavior must also be initiated strive. This means a limitation of the induk occurring overvoltages and avoidance of any oscillation tion, as these can impair or even destroy neighboring components or the power diode can lead themselves.

A limitation of the overvoltage inevitably has one slower discharge of the leakage inductance and thus an Er Increase in switching losses, so that together hang with the minimization of overvoltages and switching loss fundamentally asks the question of a compromise. It there is, however, the possibility of switching losses in the Framework of this compromise with a given maximum over voltage by varying the current or voltage curve to optimize.

The measures to ensure the desired software Depending on the starting point, recovery behavior can be defined in inter distinguish between ne and external measures.

The external measures concern corresponding modifications of the surrounding network of the power diode or its connection control. This includes, for example, the wiring of the Power diode with a so-called "snubber", that is egg ner series connection, consisting of a resistor and a Capacity. This should dampen the commutation behavior the. However, a snubber always leads to increased switching losses, a larger volume and weight of the concern the device and ultimately at a higher cost.  

Another way that is currently used to relieve performance di ode and ensure soft recovery behavior is stepped, the switching speeds to throttle the semiconductor switches involved and so the Ab to dampen commutation behavior. This would initiate the Commutation process by a controllable resistor Correspond to the position of an ideal switch. In this way it succeeds in verifying the occurrence of any overvoltage avoid and noticeably discharge the respective power diodes most. At the same time, however, the switching losses of the be divided semiconductor switches strongly.

The internal measures are essentially corresponding interventions in the design of power diodes. These interventions essentially concern the optimization of the Doping profile or lifetime setting.

The commutation behavior of a power diode in the be external measures we wrote significantly from others Components determined. This usually leads to an increase switching losses. Besides, under these circumstances only limited optimization of the power diode possible Lich. Because of this, the present Er focuses finding exclusively on the optimization of the diode design.

Usually a gentle commutation behavior is attempted by expanding the inner zone and providing one additional charge carrier reservoirs that are already in the culvert operation is to be achieved. However, this leads to the corresponding diodes to inner zone widths that are measured are oversized at the permissible reverse voltage. By this oversizing will be the forward voltages or the switching losses increased.

Furthermore, this procedure does not guarantee that the charge carrier reservoir created in the pass mode  actually the requirements of the commutation process enough. If the carrier reservoir is too small, it happens to interrupt the backflow and thus by the influence of Leakage inductances to increased overvoltages and through the Inductance caused undesirable oscillations. Is the carrier reservoir, on the other hand, is too large, so it happens correspondingly slowly decaying return currents, the so-called tail currents, and thus increased switching losses.

An alternative to this is to limit inductive overvoltage Targeted genes during the commutation process ration of load carriers and thus through controlled ent charge of the leakage inductance as soon as a certain blocking voltage is exceeded. This concept is called "field controlled-injection "or FCI for short. As a mechanism serves to generate the necessary charge carriers the shock ionization, which is the blocking capacity of a lei anyway Stungsdiode limited upwards.

The FCI concept enables load carriers to be geized as required nerated so that it automatically turns into a soft recovery Behavior comes. However, a strong lo is required calibrated load carrier generation, otherwise it would be TRAPATT- Oscillations can come.

The basic advantage of the FCI concept is that that no oversizing of the inner zone is required. This allows forward losses and switching losses against clearly above the power diodes of the type mentioned reduce.

The invention is based on the in the figures of the Exemplary embodiments illustrated in the drawing. It shows:

Fig. 1 shows a cross section through the semiconductor body of a pin-power diode with space charge coupling (in the embodiment, a read diode) according to the prior art;

Fig. 2 first embodiment of a geometrically coupled FCI diode;

Fig. 3 second embodiment of a geometrically coupled FCI diode;

Fig. 4 third embodiment of a geometrically coupled FCI diode;

Fig. 5 fourth embodiment of a geometrically coupled FCI diode;

Fig. 6 corresponding to a cross section through the semiconductor body of a geometrically coupled FCI diode 2 with the cathode side integrated blocking diode.

Fig. 7 is a circuit diagram of an FCI hybrid diode as a preferred application of an FCI diode with geometrical coupling.

Fig. 2 shows the cross section through the semiconductor body 1 an inventive geometrically coupled FCI diode. The same elements are provided with the same reference numerals according to FIG. 1.

The power diode shown in FIG. 2 contains wesentli chen the elements of a pin-power diode. The semiconductor body 1 consists of an n ^- -doped inner zone 2 . The n ⁺ doped inner zone - ^- Katho denseitig adjoins the n-doped cathode zone 3 at. The cathode zone 3 is connected to the cathode connection K via the cathode electrode 7 . The p ⁺ -doped anode zone 6 is connected on the odd side to the n ^- -doped inner zone 2 . The anode zone 6 is connected to the anode terminal A via the electrode electrode 8 .

For this purpose, in the anode-side region 2 'of the Innenzo ne 2, an additional area of higher Dotierungskonzentra tion as provided in the inner zone. 2 This additional region is n ⁺ -doped and is referred to below as floating region 5 . In the present example, the floating region 5 is formed as a buried layer.

The floating region 5 has the characteristic of a short circuit and is floating in terms of its potential. The high field cannot penetrate into the floating area 5 . The inner zone 2 is connected to the anode zone 6 via the pn junction 4 . The interface of the pn junction 4 between the inner zone 2 and the anode zone 6 is flat, ie it has no curvatures. The floating region 5 is not connected to the anode zone 6 .

By introducing the buried, floating region 5 into the inner zone 2 , a strongly inhomogeneous doping distribution is generated on the anode side. This inhomogeneous doping distribution in the anode-side region of the inner zone 2 results in a locally very different distribution of the field lines of the electric field. In particular, the field lines of the electric field preferably lead into the areas of the interface of the n ⁺ / n ^- junction 4 'between the floating region 5 and the inner zone 2 , which have the greatest curvature. At this anode-side n ⁺ / n ^- junction 4 'of the floating area 5 to the inner zone 2 , there is preferably a breakthrough.

The floating area 5 can be generated, for example, by high energy implantation as a buried layer in the inner zone 2 . Alternatively, it is also conceivable to etch anisotropically a trench into the anode-side surface of the semiconductor body 1 . A masked n ⁺ diffusion is then carried out to produce the floating region 5 .

In Fig. 3, another embodiment for a geo metrically coupled FCI diode is given. The same elements are provided with the same reference numerals in accordance with FIG. 2.

The FCI diode corresponding to FIG. 3 shows essentially the elements of the FCI diode according to Fig. 2. Here, all 6 is not arranged recently the p ⁺ doped anode zone as kontinuierli ches, homogeneous field at the front of Halbleiterkör pers. 1 Rather, the interface of the pn junction 4 between the anode zone 6 and the inner zone 2 has a curvature. Furthermore, the floating region 5 is not designed as a buried layer, but borders directly on the surface of the semiconductor body 1 . The n ⁺ -doped floating region 5 is spaced from the anode zone 6 .

As in the example in FIG. 2, the floating regions 5 also locally cause a different distribution of the doping concentrations. This also leads to an inhomogeneous distribution of the field lines of the electric field. The floating area 5 also acts as a short circuit in FIG. 3, whereby the breakdown preferably takes place in the immediate area between the anode zone 6 and the floating area 5 .

Fig. 4 shows a third embodiment of the geometrically coupled FCI diode according to the Invention. The same elements are provided with the same reference characters according to FIGS. 2 and 3.

Fig. 4 shows a further development of the geometrically coupled FCI diode corresponding to Fig. 3. Here, the n ⁺ - doped floating region 5 is no longer spaced from the anode zone 6 . Rather, the floating region 5 partially adjoins the anode zone 6 . A breakdown therefore preferably occurs at the pn junction 4 between the floating region 5 and the anode zone 6 . Furthermore, the FCI diode according to FIG. 4 has a trench 9 in the anode zone 6 . The anode electrode 8 is arranged on the surface of the trench.

The trench 9 in FIG. 4 is particularly advantageous in the production of the structures according to the invention. After anisotropic etching of the trench 9, the anode zone 6 is produced by masked diffusion. The surface of the trench is then covered over a large area with a conventional metallization. The metallization then forms the anode electrode 8 .

In FIGS. 2 to 4, the floating regions 5 are endowed much higher than the inner zone 2. Typically, the floating regions 5 have a doping concentration of max. 10 ¹⁵ cm ^-3 . The inner zone 2, however, has at least a doping concentration of 10 ¹⁶ cm ^-3 .

Since the floating regions 5 have a very high doping concentration, they act with regard to their potentials as a short circuit. Because of this, it is also conceivable to realize the float regions 5 instead of very highly doped silicon with another highly conductive material, for example polysilicon, metal silicide or metal.

In Figs. 2 to 4, a floa tendes region 5 is illustrated by way of example only, respectively. Of course, several floating areas 5 can also be provided in the power semiconductor component.

Fig. 5 shows a fourth embodiment of the geometrically coupled FCI diode according to the Invention. The same elements are provided with the same reference numerals according to the previous figures.

FIG. 5 shows a geometrically coupled FCI diode which, in contrast to FIGS. 2 to 4, has no floating region 5 . The function of the floating region 5 is replaced here by the configuration of the anode zone 6 . The anode zone 6 here has cones protruding into the semiconductor body 1 . Through these cone-like areas protruding into the semiconductor body 1 , a strong curvature of the interface of the pn junction 4 between the anode zone 6 and the inner zone 2 is generated. This curvature causes a local separation of the high field zone and the low field zone, similar to the examples from FIGS. 2 to 4. A breakdown of the electrical field takes place here preferably in the areas of the greatest curvature of the pn junction. This is typically at the top of the cone-like areas of the anode zone 6 .

Similar to FIG. 4, trenches 9 are provided in FIG. 5, which are particularly advantageous in terms of production technology. Through the trench 9 in particular the cone-like areas of the anode zone 6 can be produced in a simple manner. The trench 9 is first anisotropically etched, similar to the example in FIG. 4. Subsequently, the cone-like regions of the anode zone can be produced by masked diffusion, for example by masked diffusion.

Fig. 6 shows a geo metrically coupled FCI diode developed according to FIG. 2. The same elements are accordingly provided with the same reference numerals in the previous figures.

The FCI diode corresponding to FIG. 2 was further developed in FIG. 6 such that a further p ⁺ -doped zone 10 between cathode connection K and cathode zone 3 is seen on the cathode side. By adding an additional zone 10 in the semiconductor body 1 from FIG. 2, an additional pn junction 12 is generated. In this way, a monolithically integrated semiconductor device consisting of two antiparallel and series-connected diodes can be produced.

In principle, when generating an additional pn junction 12 by inserting an additional zone 10 into the FCI diode according to FIG. 2, care must be taken that the diode of the newly created pn junction 12 in question is anti-parallel and in series with the FCI diode is switched. In addition, it should be noted that the breakdown voltage of the additional pn junction 12 is dimensioned sufficiently high to prevent current flow in the forward direction. For this reason, in the present example, the cathode line 3 is doped less than the further zone 10 . Finally, care must be taken that the inner zone 2 adjoining the further zone 10 is dimensioned far enough so that there is no "punch-through" of the further zone 10 . In this case, the blocking effect of the additional pn junction 12 would be overridden.

It is of course also conceivable to arrange the additional zone 10 on the anode side between the anode zone 6 and the anode electrode 8 . In this case, the additional zone on the anode side would have to be n-doped and the anode zone 6 would have to be sufficiently wide.

An additional pn junction for realizing two anti-parallel diodes can of course also be generated by an anode-side or cathode-side Schott ky contact instead of another zone 10 .

Fig. 7 shows a circuit diagram of an FCI hybrid diode as an advantageous application of the FCI diode according to FIGS. 2 to 5. Between an anode connection A and a cathode connection K there is the parallel connection of the diode D ₂ and the diode D. _FCI . The diode D ₂ is, for example, a power diode optimized for good forward behavior. The FCI diode D _FCI has the function of a voltage limiter and is only effective in blocking mode. In forward operation, the diode D _FCI is blocked by the diode D ₁ connected in series and antiparallel to it. Thus, the diode D _{2 is} relevant in the forward mode and the diode D _FCI in the blocking mode.

The diodes D ₁ , D ₂ and D _FCI can be implemented as a monolithically integrated semiconductor component. However, a discrete implementation of the components is also conceivable. The advantages of a monolithically integrated arrangement lie in a low-inductance design, which in particular allows the switching losses to be reduced.

The use of FCI diodes is particularly advantageous as Free-wheeling diodes or voltage limiters connected in parallel to power semiconductor components that can be switched off, as with for example bipolar transistors, MOSFETS, IGBTs, GTOs, Thyri storen, MCTs, etc. This is both a monolithic inte Gration as well as a hybrid or discrete structure possible.

Reference list

1

Semiconductor body

2nd

Indoor zone

2nd

'' Anode-side areas of the inner zone

3rd

Cathode zone

4th

Interface between the inner zone and the anode zone

4th

'(Further) interface between the inner zone and the floating area

5

floating area

6

Anode zone

7

Cathode metallization / electrode

8th

Anode metallization / electrode

9

dig

10th

further zone

11

Coupling zone

12th

further pn transition
A anode connection
K cathode connection
D ₁

first diode; Blocking diode
D ₂

second diode; in the forward direction Lei performance diode
D _FCI

FCI diode

Claims (13)

1. Power diode consisting of a semiconductor body ( 1 ) with

• 1. an inner zone ( 2 ) of the first conduction type,
• 2 a, to the inner zone (2) adjoining the cathode zone (3) of the first conductivity type and higher doping concentration than in the inner zone (2)
• 3. an anode zone ( 6 ) of the second conductivity type and a higher doping concentration than in the inner zone ( 2 ) adjoining the inner zone ( 2 )

characterized in that

• 1. an interface ( 4 ) between the inner zone ( 2 ) and the anode zone ( 6 ) is provided, with the exception of the edge regions of the anode zone ( 6 ), where the interface ( 4 ) to the surface of the semiconductor body ( 1 ) occurs, is at least partially curved and / or
• 2. at least one floating region ( 5 ) of the first conduction type is provided in the inner zone ( 2 ).

2. Power diode according to claim 1, characterized in that the doping concentration in the floating regions ( 5 ) is higher than that of the inner zone ( 2 ). 3. Power diode according to one of claims 1 or 2, characterized in that the floating regions ( 5 ) are in the anode-side region ( 2 ') of the inner zone ( 2 ). 4. Power diode according to one of claims 1 or 3, characterized in that the floating regions ( 5 ) at least partially adjoin the on zone ( 6 ). 5. Power diode according to one of claims 1 or 4, characterized in that a further interface ( 4 ') between the inner zone ( 2 ) and the floating region ( 5 ) is at least partially curved. 6. Power diode according to one of claims 1 to 5, characterized in that the floating regions ( 5 ) consist of conductive material. 7. Power diode according to claim 6, characterized in that the floating regions ( 5 ) at least partially consist of hochdo tiert polysilicon. 8. Power diode according to one of claims 1 to 7, characterized in that in the semiconductor body ( 1 ) at least one to the power diode on tip-parallel and in series second, monolithically integrated diode is provided. 9. A method for producing power diodes according to one of claims 1 to 8, characterized in that trenches ( 9 ) on the anode side are etched into the semiconductor body ( 1 ) and then the floating regions ( 5 ) and / or the regions of the anode zone ( 6 ) with a curved interface ( 4 ) by diffusion and / or ion implantation. 10. Use of the power diode according to one of claims 1 up to 8 in hybrid diode arrangement. 11. Use of the power diode according to one of claims 1 up to 8 as voltage limiter. 12. Use of the power diode according to one of claims 1 to 8 as a freewheeling diode. 13. Use of the power diode according to one of claims 1 up to 8 in parallel to a power semiconductor device ment.